:\r.\TtYi, \M) ci'Oi.iKiK \i. sri(\i;Y IGD 



Drscrlplion.—-" ^\]v\\ >iil)()V;ii('. soiiicw liat iiilliilrd. with coiicciilric 

 transvci'so striae, vci-y (iiic near the imihoiii's, hiit iiiiicli coai'scr iicjir tin- 

 margin; ix-aks rather eh'\ate(l; IniiiiU' very iiulistiiicl ; teeth eievaletl ami 

 straight, the two posterioi' ones of the U'ft valvo pmall, much comprcsserl, 

 a|i|iri)\iiiiale. ami iieai'lv iiaiallel: ihe aiiti'i'inr lndih hirge and grooved 

 hy a (h'e|) canal: cavity of shell dee|i: margin entire; jjosterior margin 

 St raighl . and sepai^alcil from the miiscnlai' impression hy a foM or groove. 

 Length one and oiie-tciilh oT an inch; height eighty-live hundredths of 

 an inch." Rogers, 1837. 



This widely-distributed species shows great variation in outline and 

 has Ijeeii described under several names, of which only the Maryland 

 names are given in the synonymy. The complete species includes M. 

 II iilhilliojisls lleilprin with all its varieli<'s. and a nunilx'r of other Ala- 

 bama names. 



The species ranges from the base to the summit of the Maryland 

 Eocene, and is very abundant in nearly all localities. The two varieties 

 may be clearly recognized and their separation closely conforms to the 

 stratigraphic divisions. 



The form originally described by Eogers comes from the Xanjeraoy 

 formation. It is smaller, thinner, in general more elongate, and with 

 a less rounded basal margin than the older type. It was this variety 

 that Conrad afterward named liciata. 



Length, 31 mm.; width, 24 mm. 



Occurrence. — Xaxje:\[OY Foejiatiox. East and west of Port To- 

 bacco, Popes Creek, 1 to 2^ miles above Popes Creek. ^ mile below 

 Chapel Point, Upper ^Marlboro (deep cut near Chesapeake Beach E. E. 

 station), Upper Marlboro (southwest of town near forks of roads), Head 

 of Nanjemoy Creek, 1 mile southeast of Piscataway. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 Philadelphia Academy of Xatural Sciences, U. S. Xational ^Museum. 



Meeetkix gyata yak. py'ga Conrad. 

 Plate XXXIV. Figs. 2, 2a, 3, 3a, 4, 5. 



Ci/therea pi/ga Convacl, ISis, Jour. Acad. Xat. Sci. Phila., 2nd ser., vol. i, p. 131, 



pi. xiv, fiif. IS. 

 Cythcrea pijga H. C. Lea, 1S4S, Proc. Acad. Xat. Sci. Phila., vol. iv, p. 99. 



